Previous to this invention, to get a fluid sample a person was required to go to the wellhead and wait the required period of time between samples before getting a meaningful or desired sample of well fluid, as a two-phase fluid. This was very time consuming, costly, and unreliable in that exact timing was difficult to achieve among other problems. These problems prompted the design of the disclosed method for sampling a liquid from a well that will automatically capture for analysis produced well fluid, as oil for example, at specific time intervals, for detection of injected chemical solutions, for example, for indicating the arrival of the multi-phase well fluid containing one or more chemical species, as polymers, surfactants, tracers, or treating chemicals at the well. The oil samples may likewise be analyzed for the presence of surfactants. Thus, the disclosed sampler more accurately measures each fluid sample for conservation of well fluid and thus requiring discharge of less waste oil that damages the environment from the single well. Particularly, the time of arrival and the time variation of concentration of the injected chemical solution at the producing well may be determined.